(1) Field of the Invention
The invention relates to an imaging apparatus with divers resolution, and more particularly to which can perform document scanning according to a predetermined resolution setting by switching among divers image-capture elements with respective resolution defaults.
(2) Description of the Prior Art
An imaging apparatus or a scanner is one of popular computer peripherals. In an imaging apparatus, an interior image-capture unit such as a CCD is used to generate an image from a document rested upon a document plate. The image as a form of digital signals are then forwarded to a computer for further image processing or storage.
Referring now to FIG. 1, a conventional optical scanner is shown schematically. The optical scanner 1 includes a light source 10, a document carrier plate 12, a reflection lens set 14, a major lens 16 and an image-capture element 18. The light source 10 is usually a lengthy fluorescent tube for illuminating the document 2 rested upon the document carrier plate 12. The document carrier plate 12 is a transparent plate made of glass or acrylic for supporting the document 2 thereofupon. The reflection lens set 14 includes a plurality of reflection lenses, say 141, 142 and 143 for example. By providing these reflection lenses 141, 142 and 143, a proper light path for forwarding the document image can be established. In an imaging process, the reflection lens set 14 can receive and forward the document image captured from the document 2 rested upon the carrier plate 12. The document image is then sent to the major lens 16 via the reflection lenses 141, 142 and 143. In the art, the major lens 16 is a convex lens for focusing the document image to its focal point. The image-capture element 18 for capturing the document image is located right at the focal point for the major lens 16. In the art, the image-capture element 18 can be an electric charge coupling device (CCD) as an example.
Because the optical scanner is used to process document imaging and the imaging quality does highly depend upon the resolution of the image-capture element, a necessary condition for a scanner to have improved imaging quality is obvious that the scanner must include a high-resolution image-capture element. Generally, high resolution implies that the image-capture element needs to provide a huge number of pixels within a unit length of the document. Apparently, the more number of the pixels are required in the imaging process, the slower the imaging is performed.
Though a high-resolution scanner can provide better quality to the document image, yet plenty process time is required as an unavoidable tradeoff. However, for documents that the originals are already clear enough, for those that the originals include only simple drawing, or for those that clear copies are not required, a user might feel time-wasting to duplicate those document by using a high-resolution scanner. On the other hand, for the users to duplicate those documents, a simple, low-resolution and fast scanner may only meet the need. Therefore, to resolve the problem, some high-rank scanners in the market do provide a convenient switch function for the users being capable of determining if a document should apply a high-resolution imaging process or a low-resolution imaging process.
Currently, three methods as following have been applied to the switching mechanism of the aforesaid scanner. They are:                1. Integrating a zoom lens to the image-capture element;        2. Integrating a plurality of lens to the image-capture element; and        3. Integrating a plurality of lens to a plurality of image-capture elements.        
Basically, a common ideology for all three methods to achieve the operation of resolution-alternating is to vary the focus of the major lens. Among these three aforesaid methods, method 3 might need much higher cost in production due to more components being applied. On the other hand, though the application of methods 1 and 2 might need fewer components, yet a complicate switching mechanism is required to render the focus alternation.
In the early development stage of the optical scanners, the adjusting of the imaging resolution is mainly done through varying the focus of the major lens due to the higher cost and lower resolution of the image-capture element (CCD, for example). However, current image-capture technology has been improved to an extend that lower production cost and higher resolution are feasible. Hence, developing a technique of applying a single major lens to integrate several image-capture elements with various resolution will definitely contribute a lot to the market competitiveness of the product.